I. Field
The present invention relates generally to communication, and more specifically to pilot transmission schemes for wireless multi-carrier communication systems.
II. Background
A multi-carrier communication system employs multiple carriers for data transmission to a single end-point. These multiple carriers may be employed, for example, in the context of orthogonal frequency division multiplexing (OFDM) or some other multi-carrier modulation techniques. OFDM effectively partitions the overall system bandwidth into a number of (N) orthogonal subbands, which are also referred to as tones, frequency bins, and frequency subchannels. With OFDM, each subband is associated with a respective carrier upon which data may be modulated.
In a wireless communication system, data to be transmitted is processed (e.g., coded and modulated) at a transmitter and upconverted onto a radio frequency (RP) carrier signal to generate an RF modulated signal. The RF modulated signal is then transmitted over a wireless channel and may reach a receiver via a number of propagation paths. The characteristics of the propagation paths typically vary over time due to a number of factors such as, for example, fading, multipath, and external interference. Consequently, the transmitted RF modulated signal may experience different channel conditions (e.g., different fading and multipath effects) and may be associated with different complex gains and signal-to-noise ratios (SNRs) over time.
In a wireless communication system, a pilot is often transmitted from a transmitter (e.g., a base station) to a receiver (e.g., a terminal) to assist the receiver in performing a number of functions. The pilot is typically generated based on known symbols and processed in a known manner. The pilot may be used by the receiver for channel estimation, timing and frequency acquisition, coherent data demodulation, received signal strength measurements, and so on.
Various challenges are encountered in the design of a pilot transmission scheme for a multi-carrier communication system. As one consideration, since pilot transmission represents overhead in the system, it is desirable to minimize pilot transmission to the extent possible while still providing the desired performance. As another consideration, pilots needs to be transmitted in a manner such that the receivers in the system are able to detect and distinguish the pilots transmitted by the individual transmitters in the system. Moreover, the pilot transmission scheme needs to address the additional dimensionality created by the multiple carriers of the multi-carrier system.
There is therefore a need in the art for pilot transmission schemes for multi-carrier communication systems.